Gomberg–Bachmann reaction

The Gomberg–Bachmann reaction, named for the Russian-American chemist Moses Gomberg and the American chemist Werner Emmanuel Bachmann, is an aryl-aryl coupling reaction via a diazonium salt.^[1][2][3]

Gomberg–Bachmann reaction
Named after	Moses Gomberg Werner Emmanuel Bachmann
Reaction type	Coupling reaction

The arene compound (here benzene) is reacted with a diazonium salt in the presence of a base to provide the biaryl through an intermediate aryl radical. For example, p-bromobiphenyl may be prepared from 4-bromoaniline and benzene:^[4]

BrC₆H₄NH₂ + C₆H₆ → BrC₆H₄−C₆H₅

The reaction offers a wide scope for both diazonium component and arene component but yields are generally low following the original procedure (less than 40%), given the many side-reactions of diazonium salts. Several improvements have been suggested. One possibility is to employ diazonium tetrafluoroborates in arene solvent together with a phase-transfer catalyst,^[5] another is to use 1-aryl-3,3-dialkyltriazenes.^[6]

Pschorr reaction

One intramolecular variation which gives better results is the Pschorr cyclization:^[7][8][9]

The group Z can be CH₂, CH₂CH₂, NH and CO (to fluorenone^[10]) to name just a few.

See also

• Graebe–Ullmann synthesis
• Meerwein arylation
• Sandmeyer reaction